Low-temperature Diffusion Process Research Articles

Efficiency Improvement of Industrial Silicon Solar Cells by the POCl3 Diffusion Process

To improve the efficiency of polycrystalline silicon solar cells, process optimization is a key technology in the photovoltaic industry. Despite the efficiency of this technique to be reproducible, economic, and simple, it presents a major inconvenience to have a heavily doped region near the surface which induces a high minority carrier recombination. To limit this effect, an optimization of diffused phosphorous profiles is required. A "low-high-low" temperature step of the POCl3 diffusion process was developed to improve the efficiency of industrial-type polycrystalline silicon solar cells. The low surface concentration of phosphorus doping of 4.54 × 1020 atoms/cm3 and junction depth of 0.31 μm at a dopant concentration of N = 1017 atoms/cm3 were obtained. The open-circuit voltage and fill factor of solar cells increased up to 1 mV and 0.30%, compared with the online low-temperature diffusion process, respectively. The efficiency of solar cells and the power of PV cells were increased by 0.1% and 1 W, respectively. This POCl3 diffusion process effectively improved the overall efficiency of industrial-type polycrystalline silicon solar cells in this solar field.

Advanced passivation of laser-doped and grooved solar cells

In this work, we investigate the use of advanced hydrogenation and low-temperature diffusion processes (a 3 h 700 °C process after emitter diffusion) for the electrical neutralization of laser-induced defects for laser doped and grooved solar cells. Despite the laser doping and grooving (LDG) process being performed before silicon nitride passivation to avoid thermal expansion mismatch between the silicon and the silicon nitride layer, some crystallographic defects are still formed during the process. The application of a low-temperature diffusion process increases implied open circuit voltages by 14 mV, potentially due to phosphorus diffusion of dislocated regions induced during laser processing. Laser hydrogenation is shown to be capable of passivating the majority of the remaining laser-induced defects. Over 1% absolute improvement in efficiency is achieved on cells with a full area aluminum back surface field. Preliminary results with minimal optimization demonstrate efficiencies of over 19% with a full area Al back contact cell. The potential to achieve much higher voltages when used with a passivated rear is also demonstrated.

Micro-joining of Multiple Stainless-Steel Sheets into a Mechanical Element by Low-Temperature Diffusion Process

A new microjoining system of plasma surface activation and intelligent heat induction processes has been developed. This microjoining process consisted of two steps. Eight stainless steel-sheets each with a thickness of 0.01 mm was surface activated by argon and hydrogen plasmas for 600 s. The passivated oxide film thickness was reduced by this surface activation. In the second step, the stack of eight stainless steel-sheets was accurately hot-stamped and joined into a mechanical element. The intelligent induction heating unit was utilized to accomplish uniform heating of the whole stack up to 1073 K for 60 seconds. Concurrent with heating, the stack was hot-stamped and held by 30 MPa for 1800 seconds. The miniature products and members such as a micropump were fabricated by this microjoining process as an alternative process that enables as to lower the joining temperature, shorten the duration time and to reduce the production cost for high qualification of metallic micropumps.

Micro-joining of multi stainless steel sheets into mechanical element by low temperature diffusion process

A new micro-joining system has been developed with use of the plasma surface activation and the intelligent heat induction processes. This micro-joining process consisted of two steps. Eight stainless steel sheets with a thickness of 0.5 mm had surfaces activated by argon and hydrogen plasmas for 600 s. The top and bottom surfaces of the eight sheets were subjected to physical bombardment by the argon plasma and to chemical reduction by the hydrogen plasma. The passivated oxide film thickness was reduced by this surface activation. This assembly of plasma cleaned stainless steel sheets was accurately stacked into a die set for joining. In this second step, the stack of eight stainless steel sheets was accurately hot stamped and joined into a mechanical element. The intelligent induction heating unit was utilized to make uniform heating of the whole stack up to 1073 K in short for 60 seconds. In parallel with heating, the stack was hot-stamped and held by 30 MPa for 1800 seconds. The miniature products and members such as a micro-pump are fabricated by this micro-joining process as an alternative process to lower the joining temperature, to shorten the duration time and to reduce the production cost for high qualification of metallic micro-pumps.

Low temperature diffusion process using rare earth-Cu eutectic alloys for hot-deformed Nd-Fe-B bulk magnets

The low temperature grain boundary diffusion process using RE70Cu30 (RE = Pr, Nd) eutectic alloy powders was applied to sintered and hot-deformed Nd-Fe-B bulk magnets. Although only marginal coercivity increase was observed in sintered magnets, a substantial enhancement in coercivity was observed when the process was applied to hot-deformed anisotropic bulk magnets. Using Pr70Cu30 eutectic alloy as a diffusion source, the coercivity was enhanced from 1.65 T to 2.56 T. The hot-deformed sample expanded along c-axis direction only after the diffusion process as RE rich intergranular layers parallel to the broad surface of the Nd2Fe14B are thickened in the c-axis direction.

Ambient temperature dependence on superconducting properties of MgB2 wires synthesized with low temperature diffusion process

In the previous study, we investigated the Cu addition using the Mg2Cu compound and the reconsidering of heat treatment through lower temperatures and longer time treatments, the so called "Low temperature diffusion process". The critical current density (Jc) under the low magnetic field was enhanced by the "Low temperature diffusion process" compared to the conventional PIT process. In this study, transport critical current (Ic)-temperature (T)-magnetic field (B) measurements of the Cu added low temperature processed MgB2 wires were carried out in order to investigate the possibility of high temperature operation. In the Ic-T-B measurement, the samples were cooled by helium (He) gas and its temperature was controlled by the out put of the external heater. The transport Ic values of the mono-cored and 19 multifilamentary wires under the 20 K and 0 T were obtained to be above 100 A. Furthermore, the transport Ic degradation by the ambient temperature and bending strain was also investigated for a large scaled low temperature diffusion processed MgB2 cable.

ＭｇＢ２超伝導体の臨界電流特性および材料化の現状と展望 Ｍｇ２Ｃｕ化合物を添加源としたＣｕ添加ＭｇＢ２超伝導線材の高温領域における臨界電流特性

The advantages of using a MgB2 compound in fusion applications are not only higher Tc (39 K) and low cost but also lower induced radioactivity than Nb-based superconductors. However, the Jc value of MgB2 wire is lower than that of Nbbased superconducting wire, and further improvement in Jc is required for use in advanced fusion reactor applications. Furthermore, the selection of low-activation sheath material is also required to keep the low induced radioactivity property. We prepared a Cu-added MgB2/Ta/Cu mono-cored wire using a Mg2Cu compound as the source material via a low-temperature diffusion process, and the transport Jc-B performances in the 4.2 K to 20 K temperature region were measured in order to investigate the possibility of the high-temperature operation.

Superconducting properties and microstructure ofMgB2 wires synthesized with a low-temperature diffusion process

The compound MgB2 has a higher Tc value (39 K) and shorter decay time for induced radioactivity than Nb-based superconducting materials suchas Nb–Ti, Nb3Sn and Nb3Al.However, the Jc value of MgB2 wire is lower than Nb–Ti alloy superconducting wire, and furtherJc improvement is required for use in an advanced fusion reactor application. In order to improveJc properties, we tried to investigate a reconsideration of the heat treatment conditionthrough comparisons with low-temperature and long-time treatment, so-called‘low-temperature diffusion’. We confirmed that there was no reduction inTc valuescompared with conventional processes when heat treated at low temperatures and for longer times(450 °C for 200 h). Furthermore,core Jc values whenheat treated at 450 °C increased with extended heat treatment time, and then the maximum coreJc value wasfound to be over 1000 A mm−2 at 4.2 K under 5 T for the 200 h treatment sample and its value was higher than for conventionalsamples with SIC addition. From the results of SEM observation, 100 nm grain-sizedMgB2 microcrystals were densely formed in the wire core and these nanograin sizes of theMgB2 phase mightaffect the Jc improvement in the low and middle magnetic field regions. On the other hand, we tried tofabricate 100 m classed mono-cored Ta sheathed wire samples having stabilized Cu in orderto investigate the workability of the Ta-sheathed sample for possible use in an advancedfusion reactor application. We found that the wire deformation of 100 m classedwire without breaking was successful for this sample, and this result proved thegood workability and possibility of fusion application of metal Ta sheathed wire.

Influence of annealing on the optical and electrical properties of multilayered InAs/GaAs quantum dots

The characteristics of multi-layered InAs/GaAs self assembled quantum dots (SAQDs) annealed after the growth were here studied using a combination of capacitance-voltage (C-V) measurements,Raman scattering and photoluminescence (PL) spectroscopy. The combination of the results obtained with the three techniques, gave evidences that the annealing at 500º C causes the sharpness of the SAQDs interfaces, while the annealing at 600º C eliminated the SAQDs. However, the comparison with the case of single layered SAQDs, revealed a thermal stability of the last system even at an annealing temperature of 700º C, thus confirming the role of the interlayer strain in the low temperature diffusion process.

Low temperature diffusion process for fabricating optical waveguides in glass

A thermal evaporation source provides a vapour stream of metallic dopant directed at a glass substrate. The metal atoms thermally diffuse into the glass surface and are accelerated through the substrate by an electric field. The doped glass forms an optical waveguide stripe.

Reduction of grain boundary recombination in polycrystalline silicon solar cells

The possibility of increasing the carrier collection efficiency in polycrystalline silicon by means of a heavily doped region near the grain boundaries is investigated. Phosphorous dopant is preferentially introduced into the grain boundaries of p-type material by a low-temperature diffusion process. A subsequent high-temperature diffusion forms a highly n-doped skin covering each grain. The resulting junction around each grain surface collects electrons which might otherwise recombine at the grain boundaries. This grain boundary doping scheme makes possible an increase in the conversion efficiency of polycrystalline silicon solar cells in which the grain structure is columnar.

Reactions of hydrogen atoms in 6 mol dm–3 sulphuric acid. Part 2.—The transition from activation to diffusion control

The relative rates of abstraction by hydrogen atoms of hydrogen and deuterium atoms from propan-2-ol and [2H7]propan-2-ol have been studied, as a function of temperature, in 6 mol dm–3 H2SO4, using both γ-radiation and photolysis of Fe2+ as the source of H. As the temperature is decreased the expected activation control, reflected in an Arrhenius temperature dependence, gives way to diffusion control. Similar behaviour is shown for the same reactions of deuterium atoms in 6 mol dm–3 D2SO4, and for the competition between propan-2-ol and Fe2+ for hydrogen atoms. In all cases, the low temperature behaviour is inadequately described by the diffusional parameters derived in the preceding paper, and a low temperature diffusion process, with an Arrhenius temperature dependence, is proposed to explain the discrepancies. From the competition studies, absolute rate parameters are obtained for the following reactions: (i) H +[2H7]propan-2-ol (abstraction of α-D)A=(6.3 ± 0.5)× 1010 dm3 mol–1 s–1, E= 20 ± 2.6 kJ mol–1, (ii) H +[2H7] propan-2-ol, (abstraction of hydroxylic H)A=(2.5 ± 0.6)× 1010 dm3 mol–1 s–1, E= 23 ± 3 kJ mol–1, (iii) H + Fe2+, A=(1.4 ± 0.6)× 1010 dm3 mol–1 s–1, E= 14 ± 3 kJ mol–1.

Influence of nitrogen on the diffusion coefficient of hydrogen in niobium

The influence of nitrogen impurities on the diffusion coefficient of hydrogen in niobium has been measured with the help of the Gorsky-effect technique. The data can be interpreted as if nitrogen in Nb suppresses the fast low-temperature diffusion process.